Many irrigation controllers have been developed for automatically controlling application of water to landscapes. Known irrigation controllers range from simple devices that control watering times based upon fixed schedules, to sophisticated devices that vary the watering schedules according to local geography and climate conditions.
With respect to the simpler types of irrigation controllers, a homeowner typically sets a watering schedule that involves specific run times and days for each of a plurality of stations, and the controller executes the same schedule regardless of the season or weather conditions. From time to time the homeowner may manually adjust the watering schedule, but such adjustments are usually only made a few times during the year, and are based upon the homeowner's perceptions rather than the actual watering needs. One change is often made in the late Spring when a portion of the yard becomes brown due to a lack of water. Another change is often made in the late Fall when the homeowner assumes that the vegetation does not require as much watering. These changes to the watering schedule are typically insufficient to achieve efficient watering.
More sophisticated irrigation controllers usually include some mechanism for automatically making adjustments to the irrigation run times to account for daily environmental variations. One common adjustment is based on soil moisture. It is common, for example, to place sensors locally in the soil, and suspend irrigation as long as the sensor detects moisture above a given threshold. Controllers of this type help to reduce over irrigating, but placement of the sensors is critical to successful operation.
Still more sophisticated irrigation controllers use evapotranspiration rates for determining the amount of water to be applied to a landscape. Evapotranspiration is the water lost by direct evaporation from the soil and plant and by transpiration from the plant surface. Potential (i.e. estimated) evapotranspiration (ETo) can be calculated from meteorological data collected on-site, or from a similar use. ETo data from meteorological monitoring equipment located on the irrigation site is thought to provide the most efficient irrigating of the landscape, however, monitoring equipment required to obtain the ETo values is very expensive to install and operate. Therefore, most of the data for ETo calculations is gathered from off-site locations that are frequently operated by government agencies. The ETo data is then broadcast by various methods to the irrigation sites. One such system, disclosed in U.S. Pat. No. 4,962,522, issued October 1990, and in U.S. Pat. No. 5,208,855, issued May 1993, both to Marian, transmits ETo values for multiple geographic zones. Irrigation controllers receive and extract appropriate data for the local conditions, and then use the extracted data to calculate run times. Unfortunately, known controllers of this type are notoriously complicated to use, and even systems touting automatic adjustment of irrigation flow still require relatively complicated input. Systems discussed in the U.S. Pat. No. 5,208,855 patent, for example, receive the signal, and update the interval used for preset irrigation control timings rather than determine an entirely new irrigation schedule. Systems discussed in U.S. Pat. No. 5,444,611 issued August, 1995 to Woytowitz et al., automatically calculate and execute a new schedule, but the new schedule is based upon meteorological data that may not be applicable to the local conditions.
Thus, because of cost and/or complicated operating requirements, most residential and small commercial landscape sites are primarily irrigated by controllers that provide inadequate schedule modification. This results in either too much or too little water being applied to the landscape, which in turn results in both inefficient use of water and unnecessary stress to the plants. Therefore, a need still exists for a cost-effective irrigation system for residential and small commercial landscape sites, which is capable of frequently varying the irrigation schedule based upon estimates of actual water requirements.